1. Field of the Invention
The present invention related to a material which can selectively remove pathogenic substances containing leukocytes, platelets and virus from a protein containing solution.
2. Description of the Related Art
Currently in the field of medical care, the need to more drastically and selectively remove virus, leukocytes, platelets, etc. from the body fluid such as blood and plasma is increasing all the more. For example, it is an accepted criterion that the blood for transfusion should not contain virus, and that, as a rule, component transfusion should give only the blood component required for the patient and no unnecessary components. However, despite the fact that it is called component transfusion, the concentrated erythrocyte preparations in general use actually contain a large quantity of leukocytes and platelets. When such concentrated erythrocyte preparations are transfused to the patients who should frequently receive transfusion (those with aplastic anemia, hemolytic anemia, chronic hemorrhagic anemia, etc.), antibody against to leukocytes and platelets is produced, and there is also a possibility of transfusion reactions. To inhibit the generation of antibody to leukocytes and platelets and to prevent transfusion reactions, it is necessary to provide erythrocyte preparations of high purity by removing leukocytes and platelets therefrom. Recently Graft-versus-Host Disease (GVHD) is posing a problem. In this disease, the lymphocytes with division potential which are present in the transfused blood acknowledge the histocompatibility antibody of the patient as the foreign matter and attack it. For this reason as well, the demand for the blood preparations from which leukocytes are removed is on the increase. To this end, it is necessary to remove lymphocytes from the blood for transfusion by a blood filter or to destroy the division potential of lymphocytes by radiation.
In the method using radiation, 1500 rad (15 Gy) of radiation is irradiated at blood preparations containing lymphocytes (fresh blood, preserved blood, concentrated erythrocyte preparations, concentrated platelet preparations, etc.) to destroy the division potential of lymphocytes. In Japan, the irradiation to blood bags is conducted mainly by X ray operators in the radiotherapeutic room. It takes about 5 or 6 minutes to irradiate one batch. In USA and Europe, an exclusive device for irradiation at blood preparations using Cs.sup.137 as the source is commercialized. With this device, it is possible to irradiate a 400 to 500 ml blood bag in 2 to 6 minutes. According to the report by Leitman et al., a function of erythrocytes, the platelet or granulocyte is not affected at this dose (Transfusion 25 (4): 293-300, 1985). However, as this method requires expensive equipment as well as the control system administered by a person responsible for the operation, it is not a universal way for everyone to practice everywhere.
On the other hand, there is a method in which a fiber filter for filtration is used to separate leukocytes by adhering them to the filter. The method takes advantage of a property of leukocyte that it tends to adhere to somewhat hydrophobic curved surface with low curvature. Filter material is prepared by laminating porous matters or fibers with small diameter, and blood corpuscles are captured when the fluid containing blood corpuscles is passed through the filter. An advantage of this method is that it is easy to handle and inexpensive. However, since leukocytes are physically captured in this method, there is a problem that complete removal of leukocytes as in the case of irradiation cannot be expected. In other words, the removal rate is increased in fresh blood in which intense acknowledgment of leukocytes is possible while sufficient removal of leukocytes is doubtful in preserved blood which offers less recognition of leukocytes. To be more precise, the filter should has an ability of recognizing and capturing leukocytes to capture leukocytes in preserved blood.
As the adsorption separation system taking advantage of selective recognition mechanism, the column method using adhesive beads is well known. For example, there are dextran sulfate-fixed beads used in the medical field which selectively adhere and remove low density lipoprotein (LDL) from the plasma, and the affinity chromatography used as a purification technique in the biochemical field.
As a method which impart the function to selectively recognize cell, virus or biologically derived substance to the membrane surface, there is a method to take advantage of the selective recognition function of a living body, for example, antigen--antibody, enzyme--substrate and receptor on the cell surface. However, this is an expensive method since the substance used as a ligand should be biologically derived protein and is therefore vulnerable to heat and acid, making it difficult to sterilize and handle.
Zierdt and others reported that they found particles such as bacteria, erythrocytes, leukocytes, platelets and polystyrene beads could still be captured when a fluid containing the particles were filtered through a membrane having a larger pore size than the particle size (Applied and Environmental Microbiology, 1979, 12, 1166-1172). They concluded that the capture was attributable to a electrostatic interaction since particles were not captured by the membrane treated with anion surfactant, and indicated that it would be possible to adhere and capture leukocytes and platelets through electrostatic interaction by means of surface electric charge.
In this regard, there is a description in U.S. Pat. Nos. 3,242,073 and 3,352,424 on the removal of platelets having negative surface charge from a fluid by using a filter material which is prepared by electrostatically binding cationic organic poly-electrolytes to anionic filter. In Unexamined Published Japanese Patent Application No. 3-207413, a filter material which possesses quarternary ammonium groups on the surface and positive zeta potential at pH 7 is described. However, when the blood is filtered through such cationic filter, the concentration of the factors released from platelets goes up and thus deteriorates the quality of blood preparations after filtration despite the improved capture rate of leukocytes and platelets.
On the other hand, isoelectric point (pI) of many virus particles is 3-6, and thus they have negative charge in the neutral range, adhesion of virus is possible through electrostatic interaction from the water containing less impurities. As the material for removing virus, there are porous membrane and material having polycationic structure on the surface such as polyvinyl pyridinium described in Unexamined Published Japanese Patent Application No. 3-123630. However, it was difficult to selectively remove virus with conventional cationic filter since non-specific adsorption of protein to the cationic surface occurs in a solution with high protein concentration such as plasma and blood.
As a filter to remove virus from body fluid and protein containing solution, regenerated cellulose membrane described in Unexamined Published Japanese Patent Application No. 2-167232. As the pore size of this membrane is smaller than that of virus particle, virus cannot pass through the membrane. However, the transmission speed is low due to the small pore size, and clogging of the membrane often occurs.
As a material to separate virus from blood and plasma by making use of biological affinity, International Patent Publication No. WO 89/01813 describes a material in which the receptor of the virus existing on the cellular surface is fixed to its surface. However, the process of purifying receptor from cell and that of binding the receptor to the base are complicated in this method. Furthermore, the use of biologically derived component creates problems of cost, functional stability and time course change.
Though the membrane technology used for separation is a technology widely used in the industry through researches on ultrafiltration membrane, reverse osmosis membrane, ion exchange membrane, gas separation membrane and osmotic gasified membrane. However, most of them are based on the separation through the difference in concentration, pressure and potential making use of membrane pore, and there are few separation membranes designed by positively introducing selective recognition mechanism into the membrane surface.